Calcium carbide



United States Patentt) CALCIUM CARBIDE Robert Barmelee VantNess, Murray Hill, NJ., assignor toiairr Reslucfi u ompany, n o po t N w r law, .a-ic rp rati n New York No Drawing. Application October 2, 1957 t Serial No. 687,626

2 .Glaims. (Cl. 206-84) fhe present invention 1 relates to improvements in the l5 handlingiand storage, of calcium carbide.- It provides animprove ralcium carbidecontainier and also a; metho ohpaekaging ordinaryg calcium carbide whereby, theimprovedtcqmainervma-y be. Obtained.

It is well knowuiin the industry -thatrcalcium: carbide whichwhambeeni stored; in. acontainer or vesselhas a markeditendency to, generate actylene upon" standing. 'Thist afterxgeneration of; acetyleneproduces at least thesfollowingundesirableresultsz it wastes acetylene since the gas; isibeing generatedat times when it is not desired; flRl-flb zcreateszan explosive hazard since the concentration ofia-lthe .resulting-acetylene in air. approaches or exceeds the-minimum: amount necessary forv an explosive-mixture, namely. 23 acetylene in air. The specific reactions occurringc-inia container to generate acetylenecannot'be explainediwitli certainty. Ordinary calcium carbide con-i tains about 77%: calcium .carbide and 23 calcium-oxide. Originally it .wasbelieved that the surface of the carbide becomes coated :with calcium hydroxide or hydrated .cal. cium oxide, which then. reacts with the carbideto generate acetylene; that any=.water.bound to the carbide also reacts witlr the carbide to. generate acetylene; and that such reactionsioceur immediately.

. .From extensi-ve;tests, however, I have-found that'the reactions in the carbide container take place over a period 40 militant-four (4) .to fourteen (l4.) days, and 'that.the

"maximum= acetylene concentration in a container will approach: the range of 23 to 26% in a few days after the carbide-has:beempacked; The acetylene concentration canebe-removed fl) by direct purgingwith' a relatively inertrgas such -as nitrogen or (2) by a series of evacuating steps and subsequentlyfilling the space above the bed of carbide wtih an inert gas. But either method of minimiaingrtheacetylene concentration is commerciallyobjeo tionables'sinceboth require the lapse of an aging period in the container before it may be purged to removethe excess acetylene. Moreover, it has been proposed to purge avessel with nitrogen while it is intheprocess of being-packed'withcarbide in an effort to raise'the lower flammabilitydimitof the acetylene-air mixture, and thus reduce-"the possibility of an explosive mixture.- But even here, after generation of acetylene resulted in a concentration of-tfrom -18' to 26% acetylene; and in instances where the container or vessel breathed in air-at ambient temperature or-a leak developed, the acetylene concentration-resultedin an explosive mixture. This situation oecur sfpart-icularlyinmost industrial type containers'since they are not-conside1'ed airtight in'the strictest sense.

The problem'ofhandling calcium carbide safely became even more. acute, when it was. discovered that calcium carbide-in finely divided form may be utilized for treating molten ferrous metal to obtain an iron product haying improved properties and characteristics. Unfortunate ly the after generation of acetylene in a calcium carbide container increases in volume-as the size of the carbide is decreased; in other words the evolution of fififiyleue increases as the total surface area of calcium 2,899,052 Patented Aug. 11, 1959 carbide is increased. In United States Patent No. 2,577,764assigned to the assignee ofthe present applica tion, for example, there is-disclosed and claimed a process for treating molten ferrous metal containing sulphur with finely divided calcium carbideto produce a'reaction between the sulphur andcarbide. A novel method of producing. animproved'gray cast iron by treating a molten cast iron composition with an agent comprising finely divided calcium carbide is disclosed and claimed in United States application Serial No; 305,315, also assigned to the assigneeof the present application. The finely dividedcalcium carbide employed in these inventionsmay', forexample, have a Tyler standard screen or sieve analysis of minus lO-mesh and at least 50% plus IOU-mesh.-

Erom recent field experience, it was shown that a potentially hazardous explosive condition exists ima container packed with 20 meshXO calcium carbide to be usedin the..treatment of molten metal. Theafter-generation ofi acetylene from such carbide in industrial contai ners amounts :to to milliliters ofacetyleneper pound of calcium carbide. Such evolution has been measured and found to be in'the range-of-0.5% to 28.0% of the total air mixture in which the ordinary carbide is stored. ltis obvious that-in many instances-acetylene concentrations in excess of 2.4%" (lower flammability limitin air) exist in hoppers packed with finely divided or metallurgical calcium carbide, thus presenting a serious problem in the industry. The major generation of acetylene (about 85%) from the small sizes of carbide usually occurs .in the first 36 hours after packing.

It appears desirable, therefore, to avoid as far as practical an excessive generation ofacetylene from. the; calcium carbide in industrial containers which might lead to explosive violence.

One object of the present invention isto provide a novel method of storing calcium carbide safely, whereby an improved container for such material is obtained.

Another object of the invention is to eliminateany explosion hazard that may exist in calcium carbide containers.

A further object of the present invention is to provide an improved method of packaging calcium carbide whereby-the. after generation of acetylene in industrial carbide containers is arrested, or greatly minimized, so that the concentration of acetylene in the atmosphere within the container is always less than the minimum amount necessary for an explosivemixture.

Still another object is to provide a method of packing finely divided calcium carbide in a commercially sat isfactor'y manner whereby the necessity for purging-the container after its initial packing is eliminated.

These and other desirable objects and advantages of the present invention will become more apparent from the following detailed description of the invention.

This invention is based mainly on the discovery that the addition ofa small quantity of carbon dioxideto an industrial container in which finely divided calcium car bide is stored'provides a container which is free of explosive mixtures even though it may not be completely airtight. While the presentinvention is applicable to all sizes of calcium carbide, it is particularly advantageous with respect to the smaller sized calcium carbide since the after generation of acetylene increases in volume as the size of the carbide is decreased. The carbon dioxide mayjbe added in solid or gaseous form. From actual tests, it wasfound that theaddition of carbon-dioxide at the time the calcium carbide was placed in a shipping container resulted in a maximum concentration of 1% acetylene, which-is less. than one-half the usual lowerexplosive .limit of acetylene inair mixtures (2.3% FUIf-i ther, ,since theaft'er generation dfacetylenenever exceeds about 1 after any Particular period of time; a the.

necessity for purging the container after the aging period is entirely eliminated. By utilizing the present invention, therefore, the container may be sealed immediately after being freshly packed with calcium carbide.

The following examples will serve to illustrate the invention. For simplicity, the details as to amounts of calcium carbide stored in industrial containers and tested, volumes of carbon dioxide, and percentages of acetylene both after one day and after eighteen days are tabulated. In all the examples the size of calcium carbide was 20- 1nesh 0. One volume of carbon dioxide is defined as being equivalent to the volume occupied by the free air space in any particular vessel or container. Carbon dioxide was added to the container when the calcium carbide was being placed therein.

Table I Acetylene Acetylene Sample No. Calcium Carbon after 1 after 18 carbide, dioxide, day, days, pounds volumes percent percent In the above examples, the volume of carbon dioxide employed varied from three to six times the volume of the free air space within the vessel or container. These examples and additional tests indicated that optimum results are obtained when the volume of carbon dioxide is one-half /2) to six (6) times that of the free air space within the container, the preferred range of volume being between 2 and 4. It will be noted that the amount of acetylene generated after one day varied from 0.0 to 0.2%, and that the amount varied from 0.6 to 1.0% after 18 days, in sharp contrast to the 10 to 26% amount of acetylene generated after 4 to 18 days in containers as conventionally packaged in the industry. Further, since the concentration of acetylene in the novel container was well below 2.3%, no aging was required. In the tests, it was observed that the total inert gases, practically all nitrogen and carbon dioxide, ranged from 85 to 98% of the total gaseous mixture in the container. Varying ranges of oxygen content were recorded since normal atmosphere breathing occurs within the container. It was noted that the use of carbon dioxide did not detrimentally afiect either the calcium carbide or the container therefor. The actual volume occupied by the calcium carbide in any one of the sample containers was slightly more than the volume occupied by the free air space therein.

The exact manner in which carbon dioxide acts to arrest the after generation of acetylene is not fully understood. It is thought that certain sites on the calcium carbide surface are the source of the acetylene which is slowly evolved from the carbide, and that the carbon dioxide is irreversibly adsorbed on such sites. The carbon dioxide may be reacting with either the strongly bound acetylene or some other chemical substance at these sites to form a protective layer which substantially minimizes or prevents evolution of acetylene. It is also possible that the carbon dioxide additon sufiiciently stabilizes the calcium hydroxide or hydrated lime so that the water normally present in these compounds is unavailable for reacting with calcium carbide to produce acetylene. There is no doubt, however, that carbon dioxide raises the lower flammability limit of acetylene-air mixtures to about 4.0%.

When carbon dioxide was employed in gaseous form, it was delivered through a pipe extending to near the bottom of the vessel. A predetermined amount of calcium carbide was then placed in the container. After the desired amount of carbon dioxide gas had been introduced in the container, the feed pipe was removed, and the container was sealed in the conventional manner.

When carbon dioxide is used in the present invention in solid form, a small amount of calcium carbide is initially added to the vessel so as to cover the bottom; the solid carbon dioxide is then placed on top of the carbide; and calcium carbide is then added to complete the packing of the container, after which it is sealed. The amount of solid carbon dioxide added is that required to furnish the desired number of volumes measured in terms of free air space volume. In a 500 pound container, for example, optimum results are obtained when the weight of solid carbon dioxide used is from A1 pound to 3 pounds, or from 0.05% to 0.60% of the carbide by weight, the preferred weight being from 1.0 to 2.0 pounds, or from 0.20% to 0.40% of the carbide. The lid or top of the container is provided preferably with a rubber diaphragm, check valve, or the like to release the pressure within the vessel as the carbon dioxide solid sublimes. From a commercial standpoint, the use of solid carbon dioxide is preferred since it can be added with a minimum amount of effort and cost.

It is evident that utilization of the present invention makes possible the handling and storage of calcium carbide in a commercially satisfactory manner. From the standpoint of safety, the novel container for calcium carbide is safer to handle and transport than are the conventional industrial containers, since the after generation of acetylene is arrested by the use of carbon dioxide. The maximum amount of acetylene generated in applicants container is substantially less than the amount required to produce potential or actual explosions in airacetylene mixtures. Calcium carbide packed in accordance with applicants process does not deteriorate or prematurely generate a significant amount of acetylene, thus preserving the calcium carbide indefinitely until it is ready for use in the ordinary manner.

It is understood that the invention is not limited to the specific examples described herein, but may be practiced in other ways without departing from the spirit and scope of the invention as defined by the following claims.

What I claim is:

1. The method of conditioning a container for storing calcium carbide safely which comprises packing said container with finely divided calcium carbide, the carbide particles being of a fineness to pass through a 20mesh screen, adding a small but effective amount of solid carbon dioxide whereby the maximum amount of acetylene generated from said carbide is always less than about 1.0% of the gaseous atmosphere within said container, said amount of solid carbon dioxide supplying a volume of carbon dioxide gas ranging from two to four times the Volume of the free air space within said container, and sealing the container.

2. A unit for the safe handling and storage of calcium carbide comprising a sealed container, finely divided calcium carbide packed in said container, the carbide particles being of a fineness to pass through a 20-mesh screen, solid carbon dioxide in an amount sufiicient to supply a volume of carbon dioxide gas ranging from two to four times the volume of the free airspace within said container, a maximum amount of acetylene generated from said calcium carbide which is less than 1% of the gaseous mixture within said container, and said solid carbon dioxide ranging from about 0.05% to 0.60% of said calcium carbide by weight.

References Cited in the file of this patent UNITED STATES PATENTS 601,064 Roberts Mar. 22, 1 -898 FOREIGN PATENTS 112,122 Switzerland Feb. 1, 1926 {$9,305, Germany Ian. 16, 1930 

2. A UNIT FOR THE SAFE HANDLING AND STORAGE OF CALCIUM CARBID COMPRISING A SEALED CONTAINER, FINELY DIVIDED CALCIUM CARBIDE PACKED IN SAID CONTAINER, THE CARBIDE PARTICLES BEING OF A FINENESS TO PASS THROUGH A 20-MESH SCREEN, SOLID CARBON DIOXIDE GAS RANGING CIENT TO SUPPLY A VOLUME OF CARBON DIOXIDE GAS RANGING FROM TWO TO FOUR TIMES THE VOLUME OF THE FREE AIR SPACE WITHIN SAID CONTAINER, A MAXIMUM AMOUNT OF ACETYLENE GENERATED FROM SAID CALCIUM CARBIDE WHICH IS LESS THAN 1% OF THE GASEOUS MIXTURE WITHIN SAID CONTAINER, AND SAID SOLID CARBON DIOXIDE RANGING FROM ABOUT 0.05% TO 0.60% OF SAID CALCIUM CARBIDE BY WEIGHT. 